A rare World War II tank purchased by Vulcan Warbirds, a company run by Microsoft co-founder Paul Allen, was never delivered, and the company has filed a lawsuit to enforce the sale.

Vulcan Warbirds purchased the Panzer IV, a German tank, for $2.5 million as part of a July fundraising auction for the Collings Foundation in Massachusetts, SFGate reported. In the lawsuit, the company alleges that they paid $2.5 million to Auctions America, the company that handled the Collings Auction, but never received the tank.

A Collings representative told the Mercury News that the Panzer tank didn’t sell during the auction because the bids received for it were too low. Vulcan Warbirds’ representative Deborah Gunn apparently contacted the auction company after the auction was over and spoke with an employee who agreed to sell the tank for its estimated value of $2.5 million.

In the paperwork filed in court, Gunn said her company subsequently learned that Rob Collings, CEO of the Collings Foundation, said the tank was not meant to be sold in the auction.

“We never sold it," Collings told the Mercury News. "It's my understanding that Auctions America tried to return the money. Collings Foundation has not received any of this, not the $2.5 million. We would not accept it."

Collings said the foundation decided to pull the tank after the auction met its fundraising goal; the tank, he said, was a core part of the organization’s collection and the trustees decided to keep it.

"Auctions America has failed to honor our agreement and yesterday we sued it and the Collings Foundation, the former owner of the tank, to enforce our contract,” the News quoted a Vulcan Warbirds statement. “We look forward to restoring the Panzer IV Tank and having it join our Sherman tank and other historic military aircraft and vehicles at the Flying Heritage Collection."